Mutually assured destruction was a standing policy during the cold war, in which the united states and the ussr maintained and expanded nuclear arsenals beyond practical levels. what could explain such a phenomenon

The idea of mutually assured destruction was a result of political and military tensions between the US and USSR. Both of these countries built up military technologies that were capable of killing millions of citizens in just a few minutes. Both countries wanted to be able to inflict a severe amount of damage on the other in case of an attack.

This is why the phenomenon of mutually assured destruction was created, as neither country wanted to unprepared if war was to break out between these two countries.